Multi carrier modulation, is widely used in applications requiring the transmission and reception of electromagnetic energy to form a transmission system. Applications can include broadcast receivers such as cellular telephone, wireless data transmission, and point to multi point data transmission systems among others. Increased utilization of a channel in an application is often achieved with multi carrier modulation transmission techniques. In multi-carrier modulation a bit stream, or information sequence, of digital data is broken up into pieces and modulated onto carriers located at different frequencies. Transmission of the electromagnetic energy may be over a transmission line or by electromagnetic radio waves.
The design of a transmission system is one of the most complex design tasks in electrical engineering, often requiring expensive circuitry in receiver and transmitter subsystems to achieve a desired performance. Attempting to prevent noise and distortion from interfering with a signal that is being transmitted is typically why high cost circuitry is utilized in a transmission system.
However, it would be more cost effective to utilize a differing modulation scheme and construct appropriate low cost circuitry to implement it. Ideally the modulation scheme would allow the appropriate circuitry to be produced inexpensively, and still provide good performance. A common form of distortion is phase noise. Phase noise is characterized by the production of a carrier frequency that is not quite at a desired set frequency, but can deviate randomly from the desired set frequency. Typically the further a possible deviation is from a set carrier frequency, the less likely the deviation is to occur. Phase noise typically becomes worse when inexpensive transmission systems are utilized. Inexpensive frequency conversion components tend to increase phase noise. Thus it would be desirable to provide a modulation system that tends to reduce distortion, while allowing inexpensive circuitry to be utilized.